The overall purpose of the study is to explore the relation of biological factors to the symptom patterns, drug response and follow-up status of a large outpatient sample of hyperactive children. Our present study is unique in having identified one clear sub- group of children accounting for 41 percent of our severely hyperactive children, characterized by high incidence of minor physical anomalies (stigmata), abnormal obstetrical history or a history of paternal hyperactivity, and elevated plasma dopamine-beta-hydroxylase (DBH) activity. This last finding is of particular interest, as we have shown that both imipramine and methylphenidate increase plasma DBH in this population. A second association between low platelet monoamine oxidase (MAO) activity with aggressive, antisocial behavior will be explored. While this group is not as clear as our high stigmata subgroup, we have found that high platelet MAO is a predictor of clinical response to imipramine. Specifically we plan to follow up our present group of 81 hyperactive boys who have been evaluated on behavioral and physiologic grounds. In addition, repeated measurements of DBH, platelet MAO and platelet catechol-O-methyl transferase will be made. A separate group of 40 young adolescents, with current learning and behavior problems and history of hyperactivity, will be evaluated to relate pubertal change, stigmata, DBH, MAO and symptom patterns to response to imipramine. Finally, a screening study of stigmata of newborns is proposed, to test predictions concerning family of obstetrical history for this group.